The overall objective is to test preliminary findings that an alteration in the synthesis of extracellular macromolecules constitutes a principal underlying factor predisposing an embryo to cardiac septal or valvular defect. In this study the direct inductive and morphogenetic influence(s) of two glycosaminoglycans (GAG) - hyaluronate (HA) and chondroitin sulfate AC(CSAC) - as well as that of collagen is to be examined on selected stages in the formation of septal primordia utilizing organ culture of excised hearts,tissue culture of isolated septal primordia (cushion tissue) and in vivo analysis when applicable. Contributions of HA and CSAC to (1) the endocardial differentiation, (2) its transformation into cushion tissue (CT) pads via cell migration and (3) the fusion of CT pads to form septa is to be studied by administering, at the critical time, inhibitors of HA and CSAC synthesis (salicylate and 6-diazo 5-oxo-L-norleucine) and elimination of one or both GAG from the extracellular matrix (ECM) by specific enzyme degradation. Collagenous contribution(s) to the above events will be tested by the use of a specific synthetic inhibitor (alpha alpha1 dipyridyl), agents which alter its physical structure - azetidine and beta-aminoproprionitrile - and removal of it from the ECM by a purified collagenase. The macromolecules will also be tested for positive (or negative) feedback on the synthesis of ECM and the capacity to maintain the differentiated phenotype in normal CT cells as well as in those previously exposed in vivo to potent cardiac septal teratogens. Data obtained from these experiments should indicate if these extracellular macromolecules directly influence any key stages in the development of cardiac septal structures and if, in concluding experiments, their influence can be manipulated to offset impending defects induced by environmental teratogens.